The invention relates to an aluminum-clad nickel-cobalt-boron based flame spray material which is characterized by excellent bonding and workability of coated surfaces.
It is common to line metal surfaces with other metals of different mechanically superior properties to obtain the best properties of both metals, e.g. cylinders in aluminum engine blocks have been lined with iron sheets to give the benefits of the light weight of aluminum and the wear properties of iron. An improvement thereon involved flame spraying the wear surface onto the receiving surface. To ensure a secure bond between substrate and sprayed metal, it was customary to prepare the substrate by mechanical roughening. U.S. Pat. Nos. 2,588,421 and 2,588,422 made a further improvement thereon in that molybdenum was first flame sprayed onto the substrate without need for special preparation of the substrate. Thereafter a hard wear surface such as high carbon steel could be sprayed and the laminate would be securely held together.
In U.S. Pat. No. 2,875,043 there were disclosed spray-weld alloys, also known as self-fluxing alloys, comprising nickel bases which could be sprayed and which, because of a content of boron and/or silicon, act as a fluxer of the alloy and of the surface to be alloyed during subsequent fusing of a sprayed coating. Other metallic components such as chromium, iron, carbon, copper and molybdenum could also be present. In U.S. Pat. No. 2,936,229 it was taught that such self-fluxing alloys might also contain about 0.2 to 5% of aluminum and that the nickel could be replaced in whole or in part by cobalt. These modifications minimized the formation of any small pores in the coating. Other elements could also be present in minor amounts.
For certain purposes it was desired that the flame sprayed surface constitute an intermetallic compound. In U.S. Pat. No. 3,305,326 there was disclosed a powder mixture as described in U.S. Pat. Nos. 2,875,043 and 2,936,229 along with coated powder particles comprising a metal nucleus and a metal coating reactable therewith at flame spray temperatures to form an intermetallic compound. The coated powder material rendered the blend self fusing, i.e. it automatically formed a fused coating upon spraying without a separate fusing operation. In U.S. Pat. No. 3,322,515 there were described modified flame spray composite materials whose components exothermically interacted with one another when melted so as to form such intermetalic compound which was deposited upon the substrate. The heat generated by the exothermic reaction aided in the bonding, and these materials were an improvement over molybdenum for bonding other flame spray materials to the substrate. The composite could comprise separate strands of the two components, e.g. a strand of nickel and a strand of aluminum, the strands being simultaneously fed to a flame spray gun. In accordance with a preferred technique one of the components could be coated onto the other, e.g. a wire comprising a nickel core and an aluminum sheath.
These composites functioned in generally satisfactory fashion but had certain significant limitations. For example the self-fusing mixture of U.S. Pat. No. 3,305,326 did not bond very well, and required either a special substrate preparation such as roughening by grit blasting, or a preliminary layer of a bonding material such as molybdenum or exothermic composite described above.
The surfaces, while of adequate bond strength for most purposes, still imposed limitations upon the working to which the coated surfaces could be put.
It is accordingly an object of the present invention to provide flame sprayable compositions which are selfbonding and which produce coatings which may readily be worked without de-bonding.
A further object of the invention is to produce superior flame sprayed bearing surfaces.